Unfortunately, due to the way the asset custom field is stored in the database, you can't easily compare it to a date in a report. All asset custom field data, due to its very nature is stored as a varchar, and can't be directly converted to a date. Furthermore, when you go the other way and convert getdate() to a varchar you run into a date formatting issue leaving the strings not directly comparable.
This means that the report you're looking for can unfortunately not be created without employing some advanced SQL techniques, or perhaps not at all.